Making Simple Molds for Slabware Making Styrofoam Molds for a Simple Platter! Jonathan Kaplan

My son is finishing up his freshman year of high school (how could that possibly be?!), so the rapid pace at which this school year has flown by is on my mind quite a bit. This might also be the case for all of those school teachers out there.

So, I thought I'd share Jonathan Kaplan's explanation of Macy Dorf's project that would work great as a lesson plan. This technique from the Pottery Making Illustrated archive would also work great for all of you non teachers who are just looking for new ways to streamline your processes in the studio. - Jennifer Poellot Harnetty, editor

What you will need:

• 1 inch blue Styrofoam, available at home centers in 4x8 ft. sheets (one sheet can make many molds)
• Felt-tipped markers
• Straightedge or ruler
• Measuring tape
• Jigsaw with an adjustable base plate.

The first step is to make a template for the shape you wish to make in clay. This can be an oval, a square, a rectangle, or any other polygon shape. Draw an oval on a piece of matte board, Masonite, or thin plywood.

Then extend a rectangle around its perimeter as shown in figure 1. This will give the template some rigidity. Make sure to oversize the mold to account for the shrinkage of your clay body. Lay the template on the Styrofoam sheet. Measure an additional 1 inch around the perimeter of the template to make the mold sturdy and rigid and, using a felt-tipped marker, draw the perimeter of the template as well as the inside shape (figure 1).

Then, using a sharp utility knife and a ruler, cut the Styrofoam along the outside perimeter. Once this basic shape is finished, it’s time to cut the interior shape, which will then be used to form the inside of the oval platter. Using a jigsaw set at a 20° angle cut out the oval (figure 2). Remember that the saw blade needs to bevel the oval outward, so that the top of the cut is wider than the bottom. This is called ‘draft’ and allows for the easy removal of the pressed clay piece.

Remove the cut oval (figure 3) and using a piece of medium-grit sandpaper, sand the cut edge smooth (figure 4). Then place this cut piece on a larger piece of Styrofoam and cut a rectangle to correspond to the outside edge of the first mold piece. This becomes the bottom of the mold. Once cut and squared up, use duct tape along all the edges and the face to secure the bottom of the mold to the top piece with the cut oval (figure 5). Your mold is now complete! If you wish to make different shapes, now is a great time to make additional molds so that you have a variety of shapes to work with.

Making an Oval Plate

Using a slab roller or a rolling pin, roll out a slab. Macy uses a selection of SlabMats with a table top slab roller for smaller pieces. Canvas can also be used as an alternative to the SlabMats. The slab is rolled with a SlabMat on the top and the bottom of the clay. This allows the finished slab to be moved without distortion. Macy uses the outside perimeter of the Styrofoam mold to estimate an approximate size to cut the slab.

>Once the slab is prepared, he uses a small rib, moving in all directions to smooth out any marks in the slab and to compress the surface. Remember that the slab is just slightly thicker than what is desired for the finished ware since it will become thinner once it’s worked into the mold. Removing the top SlabMat, the mold is positioned upside down over the freshly rolled slab. The SlabMat is then wrapped over the mold and the entire “sandwich” is flipped over in one smooth move. The mat is removed revealing the slab as it begins to slump and conform to the cut Styrofoam oval.

Now comes the critical step of pressing the slab into the mold so that it is fully supported. Using a slightly damp sponge and his fingers, Macy deftly follows the oval cut out around its circumference and presses the moist clay into the mold. After that, he uses the same sponge to press the clay onto the flat bottom of the mold and compressing it fully around the inside perimeter and flat bottom. You can see how there is now excess clay on top of the mold. By using a needle tool or potter’s knife, the outside edge is cut away leaving an oval rim. Macy uses his fingers to trace the inside edge of the oval while cutting the excess clay away. This insures that the rim follows the contour of the interior oval (figures 6–8).

After the piece has set up, it can be safely removed from the mold by gently but swiftly flipping it onto a ware board (figure 9–10). Lastly, the piece is flipped over, the outside edge can be detailed and smoothed with a sponge or rib. To make sure the bottom does not dome up during the drying, he presses the bottom of the platter so that it stays flat.

Following this very simple process, you can now easily experiment with making multiples of different shaped platters, plates and bowls.

Macy Dorf, a well-established potter in Denver, Colorado, makes a colorful line of high-fired functional stoneware. He sells work out of his storefront in the Santa Fe Arts District as well as to galleries and craft shops in many western states. Jonathan Kaplan is a potter, designer, and gallerist living in Denver, Colorado.